1. Field of the Art
The present invention relates to an automatic redialing method for a mobile communication network and a mobile communication system. More particularly, the present invention is concerned with an automatic redialing method applicable to a mobile communication network accommodating hand phones, car phones or similar mobile terminals.
2. Description of the Background Art
In a mobile communication system accommodating mobile terminals, e.g., hand phones or car phones extensively used today, the digitization and high integration of devices have promoted the reduced size light weight configuration of the terminals. In addition, the broadening communication area and reciprocal services available between different districts have implemented conversation at any place or in any district and have further accelerated the spread of the mobile terminals.
Generally, a mobile communication system includes portable terminals or similar mobile stations, base stations each covering the mobile stations in an area on radio links, and mobile communication exchanges each accommodating a plurality of base stations for connecting a call originating from any mobile station en route to destination. The mobile communication exchanges are interconnected by transit switches, and each is connectable to a public switched telephone network or similar fixed network or to another mobile communication network via, e.g., a gateway office.
When a call originates any one of the mobile stations belonging to the above system, the mobile station acquires the reverse control channel of the base station covering the mobile station. Then, the mobile station sends an origination message including the ID (Identification) number of the called terminal over the control channel at a preselected timing. The base station having received the origination message transfers the information included in the message to the associated mobile communication exchange. At the same time, the base station sets up a communication channel between itself and the calling mobile station so as to establish a communication path between the mobile station and the mobile communication exchange.
The mobile communication exchange connects based on the received origination information, communication the path to an exchange on the called side accommodating the called terminal and in turn calls the terminal. For example, if the called terminal is a telephone terminal connected to a public switched telephone network, then the mobile communication exchange sends the origination information to the telephone network via, e.g., a gateway. When the origination information is transferred from the telephone network to a subscriber line exchange accommodating the called telephone terminal, the subscriber line exchange activates a subscriber line assigned to the telephone terminal while sending a ring tone to the calling side on the communication path. As a result, a ringing tone is generated from the telephone terminal while the ring tone is sent to the mobile station on the speech channel.
On the other hand, when the called telephone terminal is busy, the subscriber line exchange detects the busy state of the terminal and sends a busy tone to the calling side on the communication path. The user of the calling mobile station, hearing the busy tone, recognizes the busy state of the telephone terminal and hangs-up or otherwise disconnects the channel. The user of the mobile station may again call the telephone terminal later by, e.g., pressing a redial button provided on the mobile station. That is, a redialing function has customarily been implemented by manual operation.
It sometimes occurs that the channel between the mobile station and the base station cannot be set up due to channel congestion or some other similar cause. The conventional mobile station has an automatic re-setting or redialing function for coping with such an occurrence. For example, the mobile station executes the automatic re-setting or redialing function when an origination request sent from the mobile station is not acknowledged by the base station, when the mobile station fails to receive an answer from the base station despite that the base station has acknowledged the origination request, when no speech channels are assigned to the mobile station after the acknowledgement, or when the base station fails to receive an answer returned from the mobile station at the time of switching of the speech channel. In any case, the mobile station starts a timer at the same time as it sends an origination message and repeats, if a channel is not set up on the elapse of a preselected period of time, the call origination procedure until the establishment of a channel.
However, the automatic redialing function available with the conventional mobile station is limited to the establishment of a channel between the mobile station and the base station. When the called terminal is busy, the user of the mobile station must repeatedly call the desired terminal by hand, resulting in time-wasting and labor-consuming operation. Automatic redialing maybe implemented if an extra circuit for detecting a busy tone is added to the mobile terminal. However, the addition of a new circuit would obstruct the miniaturization of the mobile station and would increase the cost of the mobile station.
It is therefore an object of the present invention to provide an automatic redialing method for a mobile communication network and a mobile communication system capable of automatically redialing a desired terminal without resorting to any additional circuit.
In accordance with the present invention, an automatic redialing method for a mobile communication network allows a mobile station belonging to the network and having originated a call to redial, if a called terminal including a fixed terminal of a public network is busy, the called terminal when the busy state of the called terminal ends. The method begins with a step of causing a mobile station exchange to send, when a call originates from the mobile station, origination information including a first identification assigned to the mobile station and a second identification assigned to the called terminal to an exchange accommodating the called terminal on a control line. The exchange accommodating the called terminal stores, when the called terminal is busy, the first and second identifications and monitors the state of the called terminal. On detecting the end of the busy state of the called terminal, the above exchange sends end-of busyness information including the first and second identifications to the mobile communication exchange on the control line. The mobile communication exchange having received the end-of-busyness information transfers, based on the first identification included in the send-of-busyness information, the end-of-busyness information to a base station covering the mobile station. The base station having received the end-of-busyness signal generates a corresponding end-of-busyness message and sends the message to the mobile station on the control channel of a reverse radio channel. The mobile station having received the end-of-busyness message redials the called terminal.
Also, in accordance with the present invention, a mobile communication system accommodating a mobile station on a radio channel and connectable at least to a public network includes a base station for setting up a radio link between itself and the mobile station. A mobile communication exchange accommodating the base station connects a call originating at a mobile station to a desired link including the public network. When a call originates from the mobile station, the mobile communication exchange sends origination information including the first identification of the mobile station and the second identification of a called terminal to an exchange accommodating the called terminal on a control line. The exchange accommodating the called terminal stores, when the called terminal is busy, the first and second identifications and monitors the state of the called terminal and sends, on detecting the end of the busy state of the called terminal, end-of-busyness information including the first and second identifications to the mobile communication exchange on the control line. The mobile communication exchange includes an information generating circuit for reporting, on receiving the end-of-busyness information from the exchange, the base station covering the mobile station that the mobile communication exchange will redial the called terminal, and a redialing function for redialing the called station on the basis of the second identification to thereby set up a speech path between the mobile station and the called terminal. The base station includes a message generating circuit for generating, when informed of a redialing to occur by the mobile communication exchange, a redial message representative of the redialing to occur and capable of being sent to the mobile station. The mobile station includes a message generating function for generating, on receiving the redial message from the base station, a redial answer message if a user of the mobile station is ready to respond, and sending the redial answer message to the base station.